Ethernet is a family of computer networking technologies for local area networks (LANs). Ethernet was commercially introduced in 1980 and standardized in 1985 as IEEE 802.3 by the Institute of Electrical and Electronics Engineers (IEEE). Ethernet has largely replaced competing wired LAN technologies.
The Ethernet standards comprise several wiring and signaling variants of the Open Systems Interconnection (OSI) physical layer in use with Ethernet. The original 10BASE5 Ethernet used coaxial cable as a shared medium. Later the coaxial cables were replaced by twisted pair and fiber optic links in conjunction with hubs or switches.
The 10BASE-T Ethernet standard was designed for point-to-point links only, and all termination was built into the Ethernet device. Higher speed connections use initial auto-negotiation to negotiate about speed, half duplex and full duplex and master/slave. This auto-negotiation is based on pulses similar to those used by 10BASE-T devices to detect the presence of a connection to another device. When the auto-negotiation has finished, the devices only send an idle byte when there is no data send, to keep the link up.
Power-over-Ethernet (PoE) is an active standard (IEEE 802.3.af and IEEE 802.3.at) which allows a PoE supply to provide electrical energy to detached networked electrical consumers like routers, switches, printer spoolers, et cetera over their standard Ethernet cable connection. Here actual standardization is going to support power levels even above 50 W per Cat5 connection. Currently, discussions are coming up to use the same standard for all kinds of low power consumers like lighting equipment (sensors, switches, light sources) or entertainment appliances like active speakers, internet radios, Digital Versatile Disk (DVD) players, set-top boxes and even television (TV) sets. PoE phones and PoE powered control devices are becoming already common practice in offices.
In the industry, power distribution over network cables as covered by the PoE standard gets more and more used. Moreover, as a consequence of providing more and more LED based lighting systems, the request for efficient low cost driving architectures is high. One important application area can be lighting over Ethernet. PoE as covered in IEEE 802.3.af is based on a star network topology. However, in lighting applications, conductors with multiple loads are connected in parallel (like in track-lighting systems where spots are clamped on a track with conductor rails) or in daisy-chain where the cable from one luminaire clicks into the next and so forth. In both lighting topologies a shared medium for the network is matching the wiring schemes better. The old 10Base2 Ethernet standard was describing exactly that. But traditional PoE does only support twisted-pair wiring.
Conventional architectures use standard Cat5 Ethernet cabling, as the cables are cheaply available with preinstalled end connectors. Often the PoE standard is employed for power management. However the use of this standard does limit the solution to star topologies in wiring, as only one load can request power per port of a switch. Daisy-chaining is not easily possible as a powered device in the middle would need to offer to the next powered device a power supply unit (PSU) port that can provide power. On the other hand the device needs to indicate power requirements down/up the line to the PSU which inherently would require knowledge of the power requirements up/down the line.
FIG. 1 shows a conventional architecture of a PoE based lighting system with a central power supply device (e.g. power sourcing equipment (PSE)) 1 with a plurality of PoE enabled output ports 12. For each load device 2 one of the output ports 12 gets wired by Cat5/6 cables 3 with connectors. In the example of FIG. 1, the load device 2 is a PoE lamp that incorporates a light source 26 and a PD controller/driver 20. Other load devices could also comprise fans, sensors or user interface devices like displays or switch panels. The supply device 1 comprises a PSU controller 10 which controls for each individual output port 12 the applied voltage and monitors for over-current with respect to the power request signalled by the PD controller 20 in each load device. However, only star type wiring or topology or configuration is supported and hence an individual wiring between each and every load (lamp, sensor, . . . ) and the central PSE is required.